Effect of processing parameters on the development of anisotropic α-Al2O3 platelets during molten salt synthesis

Abstract

It is of utmost importance to control the size and morphology of anisotropic α-Al2O3 platelets owing to its extensive usage in various applications, including most recent synthetic biomimetic abalone nacre-like composites. In the present article, a wide range of well-developed and well-dispersed α-Al2O3 platelets were produced with diameter and thickness ranging from 4 - 8 μm and 0.6–1 μm respectively, by taking γ-Al2O3 precursor and sodium sulfate as low melting flux. The effects of various processing parameters like calcination temperatures, molar ratios of Al/Na and soaking time on the phase formation and morphology development of the final platelets were investigated in rigor. The results indicated that high calcination temperature of 1200 °C and moderate soaking time (60 min) helped to develop α-Al2O3 platelets with hexagonal morphology and uniform sizes. The sulfate salts created favorable conditions for growth of anisotropic platy α-Al2O3 and Al/Na molar ratio has significant effect in controlling the aspect ratio of the platelets. The impact of deagglomeration treatment by the ultrasound irradiation on the calcined aggregates of platelets was also examined. The breakage of platelets clusters by fracture/erosion due to the interaction with imploding cavitation bubbles under ultrasound energy, reached maximum after 90 min of deagglomeration treatment. The detail phase transformation sequences from γ-Al2O3 to α-Al2O3 was explained by correlating thermal (DT-TGA) and X-ray analysis. The growth mechanism of the anisotropic α-Al2O3 particles in the presence of molten Na2SO4 liquid was also unraveled.